1. Field of the Invention
The present invention relates to a surface-treating agent for forming resist patterns used in the manufacturing processes of semiconductors such as IC and the like, liquid crystals, the manufacture of circuit substrates for thermal heads and the like, and lithographic processes of other photo-fabrications, and also relates to a pattern-forming method using the same.
In particular, the present invention relates to a surface-treating agent for forming a resist pattern suitable for exposure with an immersion projection exposure apparatus using far ultraviolet rays of wavelengths of 200 nm or less as a light source, and a pattern-forming method using the same.
2. Description of the Related Art
From the advent of the resist for a KrF excimer laser (248 nm) on, an image-forming method that is called chemical amplification is used as the image-forming method of the resist for compensating for the reduction of sensitivity by light absorption. To explain the image-forming method of positive chemical amplification by example, this is an image-forming method of exposing a resist to decompose an acid generator in the exposed area to thereby generate an acid, utilizing the generated acid as the reactive catalyst to change an alkali-insoluble group to an alkali-soluble group in the bake after exposure (PEB: Post Exposure Bake), and removing the exposed area by alkali development.
With the progress of fining of semiconductor elements, shortening of the wavelengths of exposure light source and increasing of the numerical aperture of the projection lens (high NA) have advanced, and now exposure apparatus using an ArF excimer laser having wavelength of 193 nm as a light source have been developed. The degree of achievement of fining of semiconductor element can be expressed by resolution, and can be expressed by the following expression:(Resolution)=k1·(λ/NA)wherein λ is the wavelength of the exposure light source, NA is the numerical aperture of the projection lens, and k1 is the coefficient concerning the process.
As a technique for increasing resolution, what is called an immersion method of filling between a projection lens and a sample with a liquid of high refractive index (hereinafter also referred to as “immersion liquid”) has been conventionally proposed.
As “the effect of immersion”, the above resolution and depth of focus can be expressed by the following expressions in the case of immersion, taking λ0 as the wavelength of the exposure light in the air, n as the refractive index of immersion liquid to the air, and NA0=sin θ with θ as convergence half angle of the ray of light:(Resolution)=k1·(λo/n)/NA)0 
That is, the effect of immersion is equivalent to the case of using exposure wavelength of the wavelength of 1/n. In other words, in the case of the projection optical system of the same NA, the depth of focus can be made n magnifications by immersion.
As a technique for further increasing resolution, a pattern-forming method using a special process is proposed. This is equivalent to lessening k1 in the above expression of resolution. One such a process is a freezing process (JP-A-2005-197349 (The term “JP-A” as used herein refers to an “unexamined published Japanese patent application”.) and J. Vac. Sci. Technol. B 4, 426 (1986)).
As disclosed, e.g., in JP-A-2005-197349, of the processes of forming a first resist pattern on a first resist film, forming a second resist film on the first resist pattern, and forming a second resist pattern on the second resist film, the freezing process means a process of changing the property of the first resist pattern by chemical or physical treatment so that the first resist pattern does not dissolve in a second resist solution or does not mix with the second resist film in forming the second resist film. By using this technique, a desired resist pattern can be formed in parts two times, so that twice the quantity of resolution can be realized as compared with an ordinary exposure process. Here, the first and second are orders of processes to form the first layer and the second as shown in FIGS. 1A to 1L.
As the known example of the freezing process, JP-A-2005-197349 can be exemplified. In the example, after forming the first resist pattern, the property of the first resist pattern is changed by the irradiation of the first resist pattern with vacuum ultraviolet ray so that the first resist pattern does not dissolve in a second resist solution. In connection with this method, there is described in the known example that the dimension of the first resist pattern is subjected to variation before and after irradiation with vacuum ultraviolet ray. Concerning this problem, a countermeasure of compensating for the dimension of the first resist pattern is devised taking the dimensional fluctuation by irradiation with vacuum ultraviolet ray into consideration. However, it is estimated that the quantities of dimensional fluctuation differ according to the dimensions of resist patterns, and it is actually impossible to design masks compensated in dimensions of actual patterns of semiconductor devices where patterns of various dimensions and forms are present. Accordingly, as the fundamental characteristics required of the freezing process, it is necessary to reconcile (i) the first resist pattern does not dissolve in the second resist solution, and (ii) the dimension of the first resist pattern does not vary before and after the change of the property of the first resist pattern. Further, in general, in the manufacturing process of a semiconductor circuit, a resist pattern is used to transfer the pattern by etching onto a substrate with the resist pattern itself as the mask. At this time, it is required that the etching resistance of the entire resist pattern is the same in arbitrary one pattern. Accordingly, it is further required of the freezing process (iii) the dry etching resistances of the first resist pattern and the second resist pattern are the same. However, materials and processes that satisfy all of these three characteristics have not been found yet.